U.S. patent application number 09/950337 was filed with the patent office on 2003-03-13 for spiral gas flow plasma reactor.
This patent application is currently assigned to CeramOptec Industries, Inc.. Invention is credited to Neuberger, Wolfgang, Solomatine, Alexei.
Application Number | 20030047138 09/950337 |
Document ID | / |
Family ID | 25490292 |
Filed Date | 2003-03-13 |
United States Patent
Application |
20030047138 |
Kind Code |
A1 |
Neuberger, Wolfgang ; et
al. |
March 13, 2003 |
Spiral gas flow plasma reactor
Abstract
A plasma reactor and accompanying method for thin film
deposition is disclosed, comprising a system of input means and
exhaust means that produce an adjustable spiral flow of precursor
gas used in creating a spatially stable plasma over large substrate
surface areas. The flow of gas created by this configuration of
input and exhaust means results in a plasma that remains uniform as
it extends radially from the center to the edges of the substrate
and is capable of high quality depositions and high deposition
rates. In a preferred embodiment, the input means is in the form of
a ring jet with a tangential flow component surrounding the
substrate. Gas exhausts through exhaust means located at a
preselected distance above the substrate. In a preferred
embodiment, gas exhausts through a central exhaust aperture and a
number of surrounding apertures located at a preselected distance
from the central exhaust aperture. Both the central and surrounding
exhaust apertures may be connected by an adjustable manifold to
allow for coordinated positioning of the central and surrounding
apertures. Additionally, apertures located at the bottom of the
cavity can be used to input additional precursor gas so as to
maintain the spiral flow over the substrate.
Inventors: |
Neuberger, Wolfgang;
(Labuan, MY) ; Solomatine, Alexei; (Bonn,
DE) |
Correspondence
Address: |
BOLESH J. SKUTNIK PhD, JD
515 Shaker Road
East Longmeadow
MA
01028
US
|
Assignee: |
CeramOptec Industries, Inc.
|
Family ID: |
25490292 |
Appl. No.: |
09/950337 |
Filed: |
September 11, 2001 |
Current U.S.
Class: |
118/715 |
Current CPC
Class: |
C23C 16/45502 20130101;
C23C 16/511 20130101; H01J 37/3244 20130101; H01J 37/32834
20130101; C23C 16/455 20130101 |
Class at
Publication: |
118/715 |
International
Class: |
C23C 016/00 |
Claims
What is claimed is:
1. A device for plasma enhanced chemical vapor deposition of thin
films onto large substrates comprising input means and exhaust
means which create a spiral flow of precursor gas near a surface of
a substrate in a deposition chamber cavity prior to plasma
formation and during plasma enhanced deposition.
2. The device according to claim 1, wherein said input means is
positioned near said substrate and said exhaust means is located at
a preselected distance above said substrate.
3. The device according to claim 1, wherein said input means is a
hollow ring jet containing a tangential flow component located near
said substrate.
4. The device according to claim 3, wherein said tangential flow
component is achieved by use of apparatuses chosen from a group
consisting of fins and directed input nozzles.
5. The device according to claim 1, wherein said input means
consists of at least one input aperture located near said
substrate.
6. The device according to claim 1, wherein said exhaust means
comprises: a first exhaust means consisting of a central exhaust
aperture; and a second exhaust means consisting of a number of
peripheral exhaust apertures located around and near said first
exhaust means.
7. The device according to claim 6, wherein said first exhaust
means can exhaust precursor gas at a different rate than said
second exhaust means, and wherein said exhaustion rate of said
first exhaust means and said exhaustion rate of said second exhaust
means can be maintained at a preselected ratio.
8. The device according to claim 1, wherein said substrate can be
controllably moved during deposition.
9. The device according to claim 6, wherein said first exhaust
means and said second exhaust means are connected to a manifold so
as to allow coordinated positioning of said first exhaust means and
said second exhaust means.
10. The device according to claim 1, further comprising a number of
containment apertures located near said substrate to aid in
maintaining a plasma in said spiral flow above said substrate but
farther away from said substrate than said input means, and wherein
said containment apertures input precursor gas at preselected rates
of input.
11. A method of plasma enhanced chemical vapor deposition of thin
films over large substrates using a device according to claim 1,
comprising the steps of: a. creating a spiral flow of precursor gas
prior to plasma formation using input means of a precursor gas and
exhaust means of a precursor gas; b. initiating formation of a
plasma; and c. maintaining said spiral flow of precursor gas during
deposition.
11. The method according to claim 11, wherein said step of
maintaining said spiral flow of precursor gas during deposition is
accomplished by adjusting rate of input of precursor gas through
said input means and rate of exhaustion of precursor gas through
said exhaust means.
12. The method according to claim 10, further comprising the step
of: employing containment apertures through which flows additional
precursor gas, wherein said additional precursor gas flow assists
in accomplishing step c.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention concerns plasma reactors for use in commercial
processes of film deposition, etching and other processing of large
surfaces of a substrate.
[0003] 2. Information Disclosure Statement
[0004] Plasmas are useful in many processes, including surface
processing and film deposition. Plasma Enhanced Chemical Vapor
Deposition (PECVD) is a useful and effective method for thin film
deposition. Radio Frequency PECVD, in which radio frequency energy
between 3 and 30 MHz is used to strike the plasma, is useful for
deposition of silicon-based films. Microwave assisted PECVD of
diamond and diamond-like films offers the ability to produce
uniform films over larger substrate areas than hot filament CVD.
Microwave assisted PECVD is also more suitable than hot filament
CVD for high purity applications. Microwave plasma discharge is
best achieved when using precursor gas in low pressure environments
(less than 100 mm of Hg), as only then is it possible to carry out
a homogeneous discharge having a volume sufficient for processing
substrates of a significant size.
[0005] Present plasma reactors suffer from a number of significant
problems. Present plasma reactors require that the chamber be
relatively small, requiring complex cooling systems. Also, the
resultant plasmas are often uneven due to difficulty in maintaining
a uniform density in a plasma as it extends from the center of the
substrate, and thus cause uneven deposition rates and thicknesses
on the substrate. These configurations often require the use of a
rotating substrate or some other compensatory configuration to
improve the consistency of the deposition. Present radio frequency
plasma reactors, because of lower frequencies and size, often are
of a density insufficient for current processing requirements.
[0006] One attempt to alleviate these problems is described by
Besen et. al. (U.S. Pat. No. 5,501,740). In this invention,
microwave energy is introduced into a chamber via dielectric
windows, and a plasma is formed in the cavity for deposition. The
dielectric windows are positioned under the substrate holder, and
the microwave energy passes through the substrate holder from a
coaxial cable positioned under the substrate holder, forming a
plasma above the substrate. This configuration helps protect the
dielectric windows from damage due to plasma deposition, but
restricts the plasma size and the resulting potential substrate
size. The distance between the surface of the substrate and the top
of the reactor cavity can not exceed a length equal to half of the
wavelength of a microwave, in order to produce a standing wave to
increase the electric field strength in the area of plasma. The
microwave will penetrate into a plasma, which extends above the
full distance between the substrate and the top of the cavity and
quickly fades as the body of the plasma extends beyond the
substrate. Therefore, the size of a processable substrate is
limited, and it usually does not exceed an area with a diameter of
100 mm.
[0007] In another device described in German Patent DE 19802971A1,
the distance between the surface of the substrate and the top of
the reactor cavity is not limited. Microwave energy passes over the
substrate through a dielectric window ring symmetric to a central
axis of the cylindrical cavity running parallel to the cavity
walls. This configuration is potentially useful for protecting the
dielectric window and for allowing deposition on larger substrates.
Microwaves are introduced and enter the cavity in an axially
symmetric fashion. Because the microwave does not pass through the
substrate to reach the plasma zone, the distance between the holder
and the top of the cavity need not be limited, and the maximum
allowable substrate size is larger than what is possible in the
Besen configuration. Precursor gas enters the cavity through an
aperture located on the bottom of the cylindrical cavity, and
exhausts through an aperture also located on the bottom of the
cavity but positioned 180.theta. from the input aperture in
relation to the central axis of the cylindrical cavity. The plasma
under action of Archimedes' force emerges above the surface of the
substrate and loses strength and corresponding deposition rate as
it leaves the substrate. This configuration can create more than
one area of maximum electric field intensity in the space above a
substrate. This results in a plasma of non-uniform density and
deposition rates in the area above the substrate. The direction of
the flow of gas over and around the substrate is dictated solely by
the pressure differential created by exhausting gas. This
configuration limits control of the gas flow to modifications in
the volume of gas inputted or exhausted, leaving the operator
little ability to change or limit the path of the gas flow to
affect the uniformity and thickness of the deposition.
[0008] Another attempt at creating large size homogeneous thin
films, by Blinov et. al. U.S. Pat. No. 5,643,365, was created for
the purpose of creating large, rectangular shaped diamond or
diamond-like films. In that application, an extended linear plasma
in close proximity to the substrate is created with a plasma torch.
According to the patent, homogeneous depositions of diamond or
diamond-like films can be produced on large, rectangular shaped
flat surfaces by scanning the substrate along the plasma torch, or
alternatively, scanning the plasma torch along the substrate.
Potential problems still exist with this application due to the
complexity of the configuration of the apparatus and the substrate,
and can result in potential inconsistencies in deposition
thickness. Another problem with this apparatus is that it may only
be suitable for flat rectangular surfaces.
[0009] Blinov et al. discussed other previous attempts at plasma
reactors in U.S. Pat. No. 5,643,365, describing the prior
applications and the problems inherent in each previous invention.
Specifically, one application (U.S. Pat. No. 5,360,485) consists of
a cone-shaped plasma that is useful for uniform coating of a large
number of small surface areas. Its primary deficiency is its
inability to uniformly coat large flat substrates.
[0010] Other applications discussed by Blinov et. al. deal with the
creation of a ball plasma for use in deposition. The physical
geometry of such ball plasmas results in a decrease in electric
field intensity and resulting deposition thickness with increasing
distance from the substrate center. Thus, these applications also
suffer from the inability to create uniform deposition over large
substrate areas.
[0011] Therefore, a need exists to provide a method for depositing
homogeneous films, such as diamond and diamond-like films, on large
(diameters greater than 100 mm) substrates, with consistent
thicknesses in increasing radial distances from the center of the
substrate. The present invention satisfies this need.
OBJECTS AND BRIEF SUMMARY OF THE INVENTION
[0012] It is an object of the present invention to provide a method
that corrects the deficiencies of the known methods.
[0013] It is a further object of this invention to provide a device
that corrects the deficiencies of the known devices.
[0014] It is another object of this invention to provide a method
capable of producing a spiral flow of precursor gas that results in
a particularly stable plasma, resulting in a homogeneous deposition
of a desired thickness over a large substrate surface area.
[0015] It is yet another object of this invention to provide a
device capable of producing a spiral flow of precursor gas that
results in a particularly stable plasma, resulting in a homogeneous
deposition of a desired thickness over a large substrate surface
area.
[0016] Briefly stated, the present invention provides a plasma
reactor for thin film deposition and an accompanying method. The
reactor comprises a system of input means and exhaust means that
produce an adjustable spiral flow of precursor gas used in creating
a spatially stable plasma over large substrate surface areas. The
flow of gas created by this configuration of input and exhaust
means results in a plasma that remains uniform as it extends
radially from the center to the edges of the substrate and is
capable of high quality depositions and high deposition rates. In a
preferred embodiment, the input means is in the form of a ring jet
with a tangential flow component surrounding the substrate. Gas
exhausts through exhaust means located at a preselected distance
above the substrate. In a preferred embodiment, gas exhausts
through a central exhaust aperture and a number of surrounding
apertures located at a preselected distance from the central
exhaust aperture. Both the central and surrounding exhaust
apertures may be connected by an adjustable manifold to allow for
coordinated positioning of the central and surrounding apertures.
Additionally, apertures located at the bottom of the cavity can be
used to input additional precursor gas so as to maintain the spiral
flow over the substrate.
[0017] The above, and other objects, features and advantages of the
present invention will become apparent from the following
description read in conjunction with the accompanying drawings (in
which like reference numbers in different drawings designate the
same elements).
BRIEF DESCRIPTION OF FIGURES
[0018] FIG. 1--Schematic of a cross sectional view of a preferred
embodiment of the proposed invention in an illustrative
configuration.
[0019] FIG. 2--Three-dimensional view of cavity interior
represented in FIG. 1, including the spiral flow of precursor
gas.
[0020] FIG. 3--Schematic as in FIG. 1, depicting the location of
the planes perpendicular to the central axis depicted in FIGS. 4, 5
and 6.
[0021] FIG. 4--A cross-sectional view of the embodiment represented
in FIG. 1, in a plane perpendicular to the central vertical axis of
the embodiment, at a point along line A-A.
[0022] FIG. 5--A cross-sectional view of the embodiment represented
in FIG. 1, in a plane perpendicular to the central vertical axis of
the embodiment, at a point along line B-B.
[0023] FIG. 6--A cross-sectional view of the embodiment represented
in FIG. 1, in a plane perpendicular to the central vertical axis of
the embodiment, at a point along line C-C.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0024] The benefits of the present invention become evident in the
following detailed description of the present invention. This
invention is suitable for producing a variety of films, including
but not limited to diamond and diamond-like films, Silicon Oxide
and Silicone Oxide doped films, and SiO.sub.xN.sub.y films.
[0025] The most significant aspect of the present invention is a
novel plasma reactor for CVD capable of creating a spiral flow of
precursor gas over a substrate prior to plasma formation and during
plasma enhanced deposition. This spiral flow is accomplished by a
configuration of means for inputting precursor gas at controllable
input rates used in conjunction with a means for exhausting
precursor gas at controllable exhaust rates from a plasma
deposition chamber. A plasma initiated in this flow by any known
means is particularly stable, in that the operator can control the
power density or deposition rate of the plasma as it extends along
the surface of a substrate from the substrate's central axis. This
is a significant improvement over known plasma deposition
processes, in that plasmas created in these known processes
decrease in intensity from a substrate's central point and thus are
unable to consistently deposit a thin film over large substrates.
Also, this homogeneous distribution of gas over the substrate
results in a plasma capable of depositing thin films at a higher
deposition rate than is possible with the prior art.
[0026] The input and exhaust means are used in a plasma deposition
chamber cavity. The present invention is not limited to deposition
in a cavity of any particular size or shape. The input means are
located proximate to the substrate surface, both surrounding the
surface and close to the surface boundary. The input means are
movable, so as to modify the position of the gas flow relative to
the surface to achieve various deposition thicknesses or deposition
shapes. In a preferred embodiment, the input means is in the form
of one or more discreet apertures, located around the boundary of
the surface. In another embodiment, the input means is in the form
of a hollow ring jet, described more particularly in the example
below.
[0027] The exhaust means may consist of apertures through which
precursor gas will exit the deposition cavity, which are positioned
at a preselected distance above the substrate surface. In a
preferred embodiment, the exhaust means consist of one central
exhaust aperture and a preselected number of peripheral exhaust
apertures located near to and around the central exhaust aperture.
This embodiment is more particularly described in the example
below. The exhaust means are also movable relative to the substrate
surface, so as to effect the shape of the gas flow to achieve
different deposition sizes or shapes.
[0028] The central exhaust aperture is connected to a means for
varying the exhaust rate of gas through the central exhaust
aperture. The rate of exhaust through the peripheral exhaust
apertures can be varied independently from the exhaustion rate
through the central exhaust aperture. This ability to independently
vary the exhaust rate through the central and peripheral apertures
allows the operator to both create and modify the spiral flow of
precursor gas both before and during plasma deposition.
[0029] An additional embodiment consists of a preselected number of
containment apertures located around and near the substrate
surface. The containment apertures are positioned at a greater
distance from the surface than the input means. Additional
precursor gas introduced through the containment apertures before
the plasma is struck can be used during deposition to aid in
maintaining the spiral or cylindrical shape of the gas flow and to
restrict the gas flow to an area above the substrate surface.
[0030] To fully illustrate and describe the present invention, the
present invention is shown in the context of an example. This
embodiment, similar to one described in German Patent DE
19802971A1, is merely illustrative, and is not meant to limit the
availability of the invention for use in other embodiments and
configurations.
[0031] An example of a potential use of the present invention is
seen in FIG. 1, and consists of cylindrical cavity 101, located
inside cylindrical chamber 102 and containing cylindrical substrate
platform 103. Substrate platform 103 consists of substrate bearing
surface 104 and base 105, and rests in chamber 102 so that base 105
is in contact with inner floor 106 of chamber 102. Substrate 107 is
placed on substrate bearing surface 104, above which surface plasma
109 is created. Axis 113 intersects a plane containing substrate
bearing surface 104 in the center of the surface and is
perpendicular to both the plane and to interior wall 114. Microwave
energy enters cavity 101 via coaxial line 111 and through
dielectric window 237 from a microwave produced by generator 115.
This configuration offers advantages such as a larger dielectric
window area and a larger chamber volume, which aid in reducing
plasma deposition on the window. Substrate platform 103 is
connected to cooling device 117 by pipes 119 and 121, which travel
in a direction parallel to axis 113. Precursor gas enters into
cylindrical (or ring) enclosure 123 through input apertures 125,
which are connected to an external source of gas through pipe 127.
The input rate of the gas through pipe 127 can be adjusted with
input valve 128. Gas enters cavity 101 from enclosure 123 through
ring jet 129.
[0032] Precursor gas exits cavity 101 via central exhaust aperture
131 and peripheral exhaust apertures 133. peripheral exhaust
apertures 133 are connected to central exhaust aperture aperture
131 through manifold 135. The exhaustion rate of apertures 131 and
133 can be simultaneously adjusted by adjusting peripheral exhaust
valve 134. The exhaustion rate through central exhaust aperture 131
can be further adjusted relative to peripheral exhaust apertures
133 by using central exhaust valve 132.
[0033] Dielectric ring window 137 surrounds chamber 103 and is
hermetically sealed to chamber 103 by a material that does not
absorb microwaves. Window 137 is connected to coaxial line 111
through radial line 139 and coaxial line 141, ensuring axially
symmetric input of an electromagnetic wave through window 137, as
shown in FIG. 4.
[0034] Containment apertures 143, connected with a source of
precursor gas, are located at the bottom of cavity 101 and on inner
floor 106, symmetrically to axis 113.
[0035] The present device works as follows. The microwave enters
cavity 101 through dielectric window 137. A total electromagnetic
field over substrate 107 with a maximal intensity value occurs due
to axially symmetric input of microwave energy into cavity 101.
Introduction of microwaves into cavity 101 is illustrated in FIG.
5.
[0036] Precursor gas enters the cavity through ring jet 129 as a
rotating flow. Jets 125 give rotation to the flow of gas (see FIG.
6). The rotating flow of gas creates central rotary zone 145 above
the surface of substrate platform 103. The portion of entered
precursor gas that enters zone 145 travels along closed lines
created by the rotary flow. The rotary flow is also represented in
FIG. 2.
[0037] The existence in this zone of closed lines of gas current
provides prime conditions for formation and maintenance of a plasma
inside this zone. The gas enters zone 145 on the border of the
plasma. The rotary flow of gas creates a relatively large, stable,
and symmetric plasma, with a diameter approximately equal to that
of ring jet 129, that can deposit a homogeneous film of constant
thickness on the entire area of a substrate. As a result,
conditions exist for the formation of a plasma that can be
restricted to an area above the surface of substrate 107. These
conditions allow for an increased input of microwave energy, and a
resultant increased discharge capacity. The distance between a
substrate 107 and the top of chamber 103 can considerably exceed
the height of the plasma. This allows the microwave energy to enter
the plasma through all of its surface area, and as a result allows
an increase in the diameter of a substrate. The plasma is spatially
restricted and exists at a relatively large distance from the
dielectric window 137. Moving platform 103 of substrate 107 in
relation to ring jet 129 and input apertures 125 allows adjustment
of the location of central rotary zone 145 in relation to substrate
107, and thus adjustment of the size of a plasma and its influence
on substrate 107.
[0038] Through containment apertures 143, an additional flow of
precursor gas can be introduced to restrict the formation of rotary
zone 145 to an area above platform 103, to aid in maintaining the
cylindrical shape of the flow of gas above the substrate, and also
to adjust lines of a current of the basic flow of precursor gas if
necessary. The input of gas through containment apertures 143 can
be controlled by adjusting containment valve 144.
[0039] This is just a single example of a plasma reactor
configuration that could utilize a cylindrically rotating plasma.
This plasma could be used in a variety of configurations and power
sources, depending on the individual needs of the application. The
cylindrically rotating plasma offers the advantage, in many
configurations, of a more uniform and spatially restricted
deposition
[0040] The present invention is further illustrated by the
following examples, but is not limited thereby.
EXAMPLE 1
[0041]
1 Diamante film deposition Substrate diameter: 110 mm Pressure: 75
mbar Rotated gas flow through jet 129: 6 liters/min Axial gas flow
through apertures 143: 2.5 liter/min Pumped flow through aperture
131: 10% Pumped flow through apertures 133: 90%
EXAMPLE 2
[0042]
2 Diamante film deposition Substrate diameter: 150 mm Pressure: 60
mbar Rotated gas flow through jet 129: 8 liters/min Axial gas flow
through apertures 143: 3 liters/min Pumped flow through aperture
131: 20% Pumped flow through apertures 133: 80%
[0043] Having described preferred embodiments of the invention with
reference to the accompanying drawings, it is to be understood that
the invention is not limited to the precise embodiments, and that
various changes and modifications may be effected therein by
skilled in the art without departing from the scope or spirit of
the invention as defined in the appended claims.
* * * * *